Zooplankton Community Grazing Rates In Some Lakes And A Reservoir In Ethiopia

Zooplankton community grazing rate as % of algae grazed per day wasrndetermined in five lakes and one public water-supply reservoir from March, 1993 to October,rn1993_ Physical and chemical measurements (Temperature, Secchi depth, alkalin~y, salin~y etc_)rnwere taken at the same time. Radio-labelling and change in chlorophyll A (chl.a.) methodsrnwere used. Zooplankton commun~y grazing rates ranging from 0-95% day'l were obtained. Inrnsize fractionated community grazing always, the larger size zooplankters showed higherrn%G.day'1. Increase in ambient density of zooplankton resulted in increased %G.day'l in alirncases except for Lake Bishoftu in which the reverse took place. Two regression models relatingrn%G.day-l to temperature (Temp.). mean zooplankton biomass (SO), total zooplankton biomassrn(ZB), large size zooplankton biomass (UB) and total chlorophyll a (chl.a.) were tested.rnBackward deletion procedure resulted in three models which explained 27 - 64% of the totalrnvariation in %G.day'l. In both the regression models and the correlation matrices, chl.a.rnconcentration was negatively related to %G.day'1. In the later case, temperature was negativelyrnrelated to %G.day'l and ali types of zooplankton biomass. The regression coefficients were notrnsignificant at 5% significant level. Grazing results are compared with other works in temperaternand tropical regions and discussed.

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